1. Field of the Invention
The present invention relates to a machine tool controller, and specifically relates to a machine tool controller having the function of changing operation according to a motor temperature and an amplifier temperature.
2. Description of Related Art
In machine tools having a spindle and a feed axis driven by motors, an increase in a motor temperature or an amplifier temperature may cause overheating of the motor or an amplifier owing to machining conditions of the spindle such as heavy cutting or a high frequency of acceleration and deceleration, an installation environment, and the like.
As a method for preventing overheating, a servomotor control device that includes a temperature detector for detecting the temperature of a servomotor to drive a movable member, and a temperature responding controller for controlling the servomotor so as to vary an acceleration and deceleration time constant of the movable member according to the detected temperature is known (for example, Japanese Unexamined Patent Publication (Kokai) No. 2003-9563).
As another method for preventing overheating, there is known a mechanical device controlling method in which a temperature data calculator estimates the temperature of a drive unit such as a feed axis motor of a mechanical device and generates temperature data, and an acceleration and deceleration time constant calculator compares the temperature data with allowable predetermined temperature data stored in advance in a data memory to vary an acceleration and deceleration time constant of a feed axis according to the comparison result (for example, Japanese Unexamined Patent Publication (Kokai) No. 9-179623).
As yet another method for preventing overheating, there is known a motor controller in which a torque monitor monitors a torque over a predetermined time period as a load on a main motor, and a temperature estimation circuit calculates a virtual motor temperature based on an average load torque, that is, the monitoring result by the torque monitor, and a protection circuit compares the virtual temperature with a predetermined allowable temperature. When the virtual temperature exceeds the allowable temperature, a speed reduction ratio is set at 0.9 to impose a speed restriction. When the virtual temperature has been recovered, the speed reduction ratio is returned to an initial value 1.0 (for example, Japanese Patent No. 5160834).
Furthermore, as yet another method for preventing overheating, a method in which a temperature increase estimator is provided to estimate a temperature increase resulting from each of an acceleration and deceleration current and a steady current is known. According to the magnitude relationship between them, when the temperature increase resulting from the acceleration and deceleration current is predominant, the output of a spindle motor is reduced. When the temperature increase resulting from the steady current is predominant, the speed of a feed axis is reduced (for example, Japanese Patent No. 5727572).